The AI Ruler You Fear The Most...

[Blaupanzer]

One (or more) of the developers knew the Aztecs were a pushover in the first two Civ games and really beefed them up this time. Between agressiveness, military power, expansion, and culture, Montezuma's presence blocks several avenues to a win. The Germans are so aggressive that in the games I've played, they are always at war and fall behind. Germans are irritating but not a threat to victory. The Aztecs (and for some reason, the Russians) are tough to beat on score. The Aztecs also build enough culture to block that win. I shudder when I see them. (Doesn't mean I don't win, but they make it tougher.)

[bahoo]

The japanese are the most difficult in my game. Though not the toughest, they won't negotiate anything unless it's to there benefit.

It seems as though they have a lot of pride and won't ever accept peace unless you give them a technology or something of equal value so it "feels" like they won. Of course I won't do that, so I have a feeling I'll have to burn Tokyo to the ground before they except that they lost.

[Jkondrac]

Bismarck is without a doubt the toughest AI ruler. I'm playing on the easy level with all 16 civs. He is the only one that constantly takes my land. All the other civs try, but they fail. Not Bismarck. I really hope I get nukes before the game is over so I can drop a few on him...

Another ruler, that I fear is Ghandi. Not because of his strength, its because of his smarts. At least in the current game that I'm playing, Ghandi has all the civs wrapped around his finger. I can't get one civ to ally with me against him. They all love him.. It makes me sick...

[RichM]

Shaka always gives me trouble in the early game. He usually gets wiped out first though, I think he bothers the other AI's just as much as he bothers me.

[Xard]

I voted Ghandi, just because I never trust a pacifist with that many wrinkles...

As for actual hard enemies:

I normally play as the Germans, and they're pretty good for me, but I *ALWAYS* have the Russians nearby, and their expansionism kicks my ass. Its only in my most recent game of the last 4 or so that I've been able to hold them off, and then launch a counter attack and take Moscow. Now Cathy's empire is split in two and is coming over to me in droves from Cultural differences. Good ole Democracy

In a game as the Persians, I had to deal with Lincoln, and he was pretty nasty as well. He seemed to think that my land was his land, or something like that.

[ixnay]

Well, for some reason I usually end up between the French and germans, and both are bastards. If I go to war with one of them, they'll get the other to back them up. In all my game the Zulus have been stuck with a crappy start location (usually on some peninsula that is nothing but tundra) so they don't give me much trouble.